Process and device for reading radiation image information stored on an image medium by detecting both the luminescent light emitted and the reflected read out light

ABSTRACT

The invention relates to a method and a device for reading out radiation image information stored on an image medium ( 12 ). A scanning unit ( 10 ) has a laser ( 16 ) for scanning the image medium ( 12 ) with a readout light beam ( 22 ). The read/processing device ( 14 ) functions with two channels so that the luminescent light emitted by the image medium ( 12 ) during scanning and also the reflected read-out light are synchronously detected, evaluated and correlated. The digital luminescent light image values are corrected according to the digital reflection light values in order to better obtain the radiation image information.

CROSS REFERENCE TO RELATED APPLICATION

This application is a national stage of PCT/EP98/08323 filed Dec. 18,1998 and based upon DE 198 03 588.8 filed Jan. 30, 1998 under theInternational Convention.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention concerns a process and a device for readout radiationimage information stored on an image medium, in particular a phosphorusstorage plate coated with a crystalline storage substance, imaged byexposure to high energy radiation.

2. Description of the Related Art

In known devices of this type an image medium for receiving a radiationimage is radiated for example in an electron microscope, and is thenoptically read in a separate readout device by scanning underluminescence-excitation. The utilized image medium have a high dynamic,however the image quality is compromised by inhomogeneities in the imagelayer. One problem is comprised therein, that images of different scanshave a displacement or offset with respect to each other as a rule onthe basis of differing orientations of the image medium in the readingdevice. A further problem is comprised in the unambiguous identificationof the individual employed image plates.

SUMMARY OF THE INVENTION

Beginning therewith, it is the task of the invention to improve aprocess and a device of this type, such that the radiation imageinformation can be read out reliably and with low affliction of errors.A high quality should also be guaranteed, especially in the case of highradiation intensities wherein static noise artifacts occur in thebackground as opposed to systematic errors on the basis of image mediuminhomogeneities.

The invention is based on the discovery, that the light reflected fromthe image medium can be correlated with the luminescence light andtherewith can be used complimentary or supplementary for evaluating theradiation image information. In accordance therewith, it is envisionedfor the process aspect of the solution of the above-mentioned task, thatduring scanning of the image plate, the reflectioned readout light iscontinuously monitored as a reflection signal, and the reflection signalis converted into digital reflection values in synchrony with the imagesignal. Therewith, the detected values can be clearly associated and beevaluated with respect to correlation. Generally, from the processing ofthe reflection light, there results an information gain, which in theend makes possible a substantial increase in the range of employment ofthe image media.

A particularly advantageous aspect is comprised therein, that the imagevalues for obtaining the radiation image information allow themselves tobe corrected in accordance with the magnitude of the reflection value.This can generally occur by determining from the reflection value thecorrection value to be associated with the image points, and that theimage value is scaled or graduated image-point-wise with the correctionvalue.

It is further of particular advantage, when a reference image isproduced by a homogenous surface radiation of the image medium.Therewith it is above all possible to clearly determine correlationsbetween the parallel determined image- and reflection value by aone-time measurement, and to utilize this for correction or as the casemay be processing of various non-homogenous working images.Advantageously correlation data (a_(k),K) are thereby determined fromthe image values B_(R)(z,φ) and reflection values R_(R)(z,φ) of thereference image, and the image values B(z,φ) of a working image arecorrected according to the values from the stored correlation data(a_(k),K) associated reflection values R(z,φ).

It is particularly advantageous when the correlation data from the imageand reflection values of the reference image are determined in theFourier area. For this the variance of the values

B′ _(R)(z,φ)=B _(R)(z,φ)·[a _(k) ·F ₂ ⁻¹ {F ₂ {R _(R)(z,φ)}·K(u,v)}]⁻¹

are minimized, wherein B′_(R) refers to the corrected image value of thereference image, a_(k) refers to a correlation factor to be varied,K(u,v) corresponds to varying correlation coefficients in the Fourierarea, F₂ corresponds to a two-dimensional Fourier transformation and F₂⁻¹ corresponds to the inverse transformation. With the correlationsdetermined in this manner the image values B(z,φ) can be corrected fromthe working images in accordance with the equation or relationship

B′(z,φ)=B(z,φ)·[a _(k) ·F ₂ ⁻¹ {F ₂ {R _(R)(z,φ)}·K(u,v)}]⁻¹

wherein B′(z,φ) corresponds to the corrected image value of the workingimage, a_(k) and K(u,v) corresponds to the determined and the storedcorrelation data, F₂ corresponds to the two dimensional Fouriertransformation and F2⁻¹ refers to the inverse transformation.

A further advantageous aspect of the reflection signal evaluation iscomprised therein, that a working and a reference image can becorrelated to each other with respect to common scanning coordinates.Therewith the various possible fixing positions of the image medium inthe read-out device can be mathematically taken into account, so that animage correction on the basis of previously determined data with respectto given image point coordinates is possible. For this it isadvantageous, by cross-correlation of the reflection values R, R_(R) ofa working and a reference image, to determine the translation vector{right arrow over (r)} and rotation angle α of a one-to-the-otherassociated image points of the working and the reference image mappedcoordinate transformation.

A doubled correction with respect to the errors from inhomogeneities ismade possible thereby, that from the image values B, B_(R) of a workingand a reference image according to the measurement of the associatedreflection values R,R_(R) corrected image values B′,B′_(R) are produced,the corrected image values B′,B′_(R) to are rectified each other, andthe rectified or aligned corrected image values B″ of the working imageare scaled or graded with the rectified or aligned corrected imagevalues B″_(R) of the reference image.

A further advantageous aspect of the reflection light determination iscomprised therein, that by comparison of the reflection values R of aworking image with stored reflection values R_(R) of reference images ofvarying image mediums the particular image medium employed for recordingthe working image can be identified on the basis of positionallycorrelated inhomogeneities of the storage layer.

In respect to a device, it is proposed to solve the inventive task byproviding in the reading/processing device a second photo-detector forsensing the readout light reflected by the image medium during scanning,and a second analog/digital converter for converting this startingsignal into a digital reflection value R(z,φ). The two channeldetermination makes possible an evaluation of the correlation betweenthe luminescence and the reflection light signal. In order to clearlyassociate the digitized value of the two channels to each other, a clockpulse generator is provided for synchronized controlling of the twoanalog/digital converters. Therewith one working and one reflectionvalue can be produced at the same time at each clock pulse signal andvia the instantaneous scanning coordinates an image point can be fixed.

BRIEF DESCRIPTION OF THE DRAWINGS

In the following the invention will be described in greater detail onthe basis of the embodiment shown in schematic manner in the figures.There is shown in

FIG. 1 a device for reading radiation image information stored on animage medium plate;

FIGS. 2a through 2 c diagrams showing the correction of a radiationimage; and

FIGS. 3a and 3 b a diagrams for illustrating the rectification(alignment) of a radiation image.

DETAILED DESCRIPTION OF THE INVENTION

The device shown in FIG. 1 is comprised essentially of a scanning unit10 for optical scanning of an image or, as the case may be, a phosphorusstorage plate 12 and a reading/processing device 14 for reading andprocessing the radiation image information stored in the image medium 12by previous radiation exposure, for example by means of an X-ray deviceor an electron microscope, and recalled again by light radiation.

The scanning unit 10 includes a readout light source in the form of alaser 16, and scan device 18,20 for producing relative movement betweenthe readout light beam 22 produced by the laser 16 and the image medium12, so that the upper surface formed by a crystalline storage layer ispoint-by-point painted over by the incident readout light beam 22. Forthis the scanning device 18, 20 includes a rotatable scanner shaftadapted for receiving the image medium 12 on the outer casing inpositionally defined manner and rotatable by means of motor 24 about itscentral axis, and a scanner head 20 carrying the laser 16 aimed againstthe jacket surface and moveable via spindle drive 26 in the axialdirection of the scanning shaft. The instantaneous scanned position ofthe read out light beam 22 is a product of the rotation position φ ofthe scanner shaft and the displacement position z of the spindle drive26 in a cylinder coordinate system, and can be determined by a not-showncontroller for the motors 24, 26.

The readout light beam 22 stimulates on the image medium 12 the emissionof luminescence light, of which the intensity depends upon the storedradiation image information. For readout the luminescence light thescanner/processor device 14 includes a first signal channel, which isformed by a first photo-detector constructed as a photo-multiplier 28, afirst signal amplifier 30 connected on the input side with the imagesignal providing photo-multiplier 28, and a first analog-digitalconverter 32 acted on by the output signal of the signal amplifier 30.An optical filter 34 ensures that only the luminescence light istransmitted in the entry cross-section of the photo-multiplier 28.

In order to detect the reflected portion of the read out light duringscanning of the image medium 12, the scanning/processing device 14includes a second signal channel, which is comprised of a photo-detector36 constructed for example as a photodiode, a second signal amplifier 38connected on the input side with the reflection signal delivering secondphoto-detector 36, and a second analog/digital converter 40 acted on bythe output signal of the second signal amplifier 38.

For processing the digital data the scanning/processing device 14includes an image computer 42, which is connected to a storage means 44.Further, the image computer 42 is coupled to a clock pulse generator 46,which synchronously hits on the two analog/digital converters 32, 40with clock time pulses depending upon the scan coordinates. At eachclock time impulse the luminescence image signals are converted by thefirst analog-digital converter 32 into digital image values B and thereflection signals are converted via the second analog-digital converter40 into digital reflection values R and assigned in the image computer42 the image point 48 on the image medium 12 defining momentary scancoordinate z,φ. As a consequence of the luminescence emission theinformation stored on the image medium 12 is “erased”, so that the imageplate 12 is ready to be used again for new exposure to a radiationimage.

For correction of the systematic image errors, which are caused byinhomogeneities in the image layer of the image medium 12, the radiationimage information can be processed in the image computer 42. Therein useis made of the discovery, that the intensity of the reflected readoutlight depends upon how far the readout light beam can penetrate into theimage plate 12 and excite a luminescence center to emission. Thereinpositive or negative correlations in the signal strength of the imageand reflection signal can occur respectively depending on the outersurface of the image plate 12 and the internal medium characteristics.These correlations allow themselves to be used in order to correct theimage value B(z,φ) according to the measure of the reflection valueR(z,φ) using the computer. Generally the image point associatedcorrection values C(z,φ) are determined therein in dependence upon thereflection value R(z,φ), with which the image values B(z,φ) allowthemselves to be scaled image-point-wise according to the equation

B′(z,φ)=B(z,φ)·[a _(k) ·C(z,φ)]⁻¹  (1)

wherein B′(z,φ) corresponds to the corrected image value and a_(k)corresponds to a correlation factor.

The above described correlations preferably allow themselves to bedetermined thereby, that a reference image is produced by surfacehomogenous radiation of the image plate. Inhomogeneities of the imageplate 12 can then be detected by corresponding deviations of the imageand reflection value. This can be employed for cleansing variousrecorded working images with respect to the systematic errors caused byinhomogeneities. Generally this can be achieved thereby, that first fromthe image values B_(R)(z,φ) and reflection values R_(R)(z,φ) of thereference image correlation data (A_(k),K) are determined. Thesereflection values R_(R)(z,φ) of a working image can then be associatedwith the correlation data, in order to subsequently correct the imagevalues B(z,φ) of the working image according to the value of thecorrelated reflection value.

For determination of the correlation data, in place of the evaluationsof space-position correlations, the fourier components of the image andreflection signal can be drawn upon and in certain cases be subjected toa frequency correction. This can advantageously be accomplished by aprogram routine in an image calculator 42 for example with calculationof the smallest error square with which the variance of the values

B′ _(R)(z, φ)=B _(R)(z,φ)·[a _(k) ·F ₂ ⁻¹ {F ₂ {R_(R)(z,φ)}·K(u,v)}]⁻¹  (2)

is minimized, wherein B′_(R) corresponds to corrected image values ofthe reference image, a_(k) corresponds to a correlation factor to bevaried, K(u,v) corresponds to a correlation co-efficient to be varied inthe fourier area (u,v), F₂ corresponds to a two dimensional fouriertransform and F₂ ⁻¹ corresponds to an inverse transformation. With thecorrelation data obtained according to equation (2) and fixedlyassociated with image medium 12 there can then according to equation (1)the image values B(z,φ) of working images be corrected using theequation

B′(z,φ)=B(z,φ)·[a _(k) ·F ₂ ⁻¹ {F ₂ {R _(R)(z,φ)}·K(u,v)}]⁻¹  (3)

In FIG. 2 there is shown the result of the correction process accordingto equation (3) for a line shaped scanned number of discrete individualdata represented as a continuous line. By evaluation of the reflectionvalues it is further possible to correlate the working and referenceimages with respect to common scan coordinates to each other, wherebydeviating orientations of the image medium 12 on the scan shaft 18 inthe case of varying scans allow themselves to be computer compensated.For this, using the already known calculations for cross-correlation ofthe reflection value of a working and reference image, the translationvector {right arrow over (r)} and rotation angle α of a coordinatetransformation can be determined, which images or maps the associatedcorrelated image points of the working and reference image to eachother. From FIG. 3b this proceeds for a number of line shaped scannedreflection values R of a work image and R_(R) of a reference image (FIG.3a), under the presumption that the correlation co-efficient ρ exhibitsa maximum at {right arrow over (r)}=5, corresponding to an imagedisplacement in the z-direction of five image points.

The two channel determination of luminescence and reflection light canthus be used in order in a doubled image correction first from the imagevalues B,B_(R) of a working and reference image according to equation(1) or as the case may be (3) to produce a corrected image valueB′,B′_(R), and then to align or rectify the corrected image valuesB′,B′_(R) to each other, and finally to scale or graduate the aligned orrectified corrected image values B″ of the work image with the rectifiedcorrected image value B″_(R) of the reference image according to theequation $\begin{matrix}{B^{\prime\prime\prime} = \frac{B^{\prime\prime}}{m \cdot B_{R}^{\prime\prime}}} & (5)\end{matrix}$

wherein m is a constant factor.

Finally it is also possible by comparison of the reflection value R of aworking image with stored reflection values R_(R) of reference images ofvarying image plates to identify the particular image plate used for thetaking of the working image.

In summary the following is to be concluded: The invention relates to amethod and a device for readout radiation image information stored on animage medium 12. A scanning unit 10 has a laser 16 for scanning theimage medium 12 with a readout light beam 22. The read/processing device14 functions with two channels so that the luminescent light emitted bythe image medium 12 during scanning and also the reflected read-outlight are synchronously detected, evaluated an correlated. The digitalluminescent light image values are corrected according to the digitalreflection light values in order to better obtain the radiation imageinformation.

What is claimed is:
 1. A process for reading radiation image informationstored on an image medium (12), wherein the radiation image informationis formed by high-energy radiation of a phosphorus storage plate coatedwith a crystalline storage substance, the process including the stepsof: scanning the image medium with a readout light beam, wherein thereadout light beam comprises a laser beam; continuously detecting anemitted luminescence light as an image signal; determining animage-point defined by scanning coordinates (z,φ) converting the imagesignal into a radiation image information containing digital imagevalues B(z,φ), continuously detecting a readout light reflected duringthe scanning of the image medium as a reflection signal; converting thereflection signal in synchrony with the image signal into digitalreflection values R(z,φ); determining from the reflection value R(z,φ) acorrection value C (z,φ) to be associated with the image-point; andscaling the image values image-point wise with the correction values. 2.Process according to claim 1, further comprising producing a referenceimage by surface homogenous radiation of an image medium (12), andseparately processing images taken on the image medium (12) after orbefore the reference image by at least one of means of the storedreflection values R_(R)(z,φ) and image values B_(R)(z,φ) of thereference image or data derived therefrom.
 3. Process according to claim2, further comprising: determining correlation data (a_(k),K) from theimage values B_(R)(z,φ) and reflection values R_(R)(z,φ) of thereference image, and correcting the image values B(z,φ) of a work imageaccording to the magnitude of the stored reference values R(z,φ). 4.Process according to claim 2, wherein during evaluation of thereflection values R,R_(R) a work and a reference image are aligned orrectified with respect to each other with reference to common scancoordinates.
 5. Process according to claim 4, further comprisingproducing corrected image values B′,B′_(R) from the image values B,B_(R) of a work and a reference image, in accordance with the magnitudeof the associated reflection value R,R_(R), wherein the corrected imagevalues B′,B′_(R) are aligned or rectified to each other, and wherein analigned or rectified corrected image values B″ of the work image isscaled with an aligned or rectified corrected image values B″_(R) of thereference image.
 6. Process according to claim 2, wherein via thecross-correlation of the reflection values R, R_(R) of a work and areference image, the translation vector {right arrow over (r)} androtation angle α of a coordinate transformation is determined mappingthe corresponding associated image points of the work and referenceimages to each other.
 7. A process for reading radiation imageinformation stored on an image medium, wherein the radiation imageinformation is formed by high-energy radiation of a phosphorus storageplate coated with a crystalline storage substance, the process includingthe steps of: scanning the image medium with a readout light beam,wherein the readout light beam comprises a laser beam; continuouslydetecting an emitted luminescence light as an image signal; determiningan image-point defined by scanning coordinates (z,φ); converting theimage signal into a radiation image information containing digital imagevalues B(z,φ), continuously detecting a readout light reflected duringthe scanning of the image medium as a reflection signal; converting thereflection signal in synchrony with the image signal into digitalreflection values R(z,φ); determining from the reflection value R(z,φ) acorrection value C(z,φ) to be associated with the image-point; scalingthe image values image-point wise with the correction values; producinga reference image by surface homogenous radiation of an image medium(12); and separately processing images taken on the image medium afteror before the reference image by at least one of means of the storedreflection values R_(R)(z,φ) or image values B_(R)(z,φ) of the referenceimage or data derived therefrom; wherein for determining the correlationdata (a_(k),K) from the image and reflection values the variance of thevalues B′ _(R)(z,φ)=B _(R)(z,φ)·[a _(k) ·F ₂ ⁻¹ {F ₂ {R_(R)(z,φ)}·K(u,v)}]⁻¹ is minimized, wherein B′_(R) corresponds tocorrected image values of the reference image, a_(k) corresponds to acorrelation factor to be varied, K(u,v) corresponds to a correlationco-efficient to be varied in the Fourier area (u,v), F₂ corresponds to atwo dimensional Fourier transform and F₂ ⁻¹ corresponds to an inversetransformation.
 8. A process for reading radiation image informationstored on an image medium, wherein the radiation image information isformed by high-energy radiation of a phosphorus storage plate coatedwith a crystalline storage substance, the process including the stepsof: scanning the image medium with a readout light beam, wherein thereadout light beam comprises a laser beam; continuously detecting anemitted luminescence light as an image signal; determining animage-point defined by scanning coordinates (z,φ); converting the imagesignal into a radiation image information containing digital imagevalues B(z,φ), continuously detecting a readout light reflected duringthe scanning of the image medium as a reflection signal; converting thereflection signal in synchrony with the image signal into digitalreflection values R(z,φ); determining from the reflection value R(z,φ) acorrection value R(z,φ) to be associated with the image-point; andscaling the image values image-point-wise with the correction values;producing a reference image by surface homogenous radiation of an imagemedium (12); and separately processing images taken on the image mediumafter or before the reference image by at least one of means of thestored reflection values R_(R)(z,φ) or image values B_(R)(z,φ) of thereference image or data derived therefrom; wherein by comparison of thereflection values R of a work image with stored reflection values R_(R)of reference images of various individual image substrates the specificimage substrate (12) used for production of the work image isidentified.
 9. A device for reading radiation image information storedon an image medium, wherein the radiation image information is formed bythe high energy irradiation of a phosphorus storage plate coated with acrystalline storage substance, the device comprising: a) a scanner unitfor scanning an image, wherein the scanner comprises a laser forscanning the image medium by means of a readout light beam and a scandevice; b) a reading/processing device for reading and processing theradiation image information stored in the image medium, thereading/processing device having: a first photo-detector for detectingas an analog image signal the luminescence light emitted during thescanning of the image medium; a first analog-digital converter forconversion of the image signal into radiation image informationcontaining digital image values B(z,φ); a second photo-detector fordetecting the readout light reflected during the scanning of the imageplate during scaning; a second analog-digital converter for convertingthis output signal into digital reflection values R(z,φ); c) an imagecomputer to determine an image-point associated correction value C(z,φ)from the reflection values R(z,φ), and which scales image values B(z,®)image-point-wise with the correction values.
 10. Device according toclaim 9, wherein the scanner/processor device (14) includes a clockpulse generator (46) for synchronizing the control of the first andsecond analog-digital converters (32,40).
 11. A process for readingradiation image information stored on an image medium, wherein theradiation image information is formed by high-energy radiation of aphosphorus storage plate coated with a crystalline storage substance,the process including the steps of: scanning the image medium with areadout light beam, wherein the readout light beam comprises a laserbeam; continuously detecting an emitted luminescence light as an imagesignal; determining an image-point defined by scanning coordinates(z,φ); converting the image signal into a radiation image informationcontaining digital image values B(z,φ), continuously detecting a readoutlight reflected during the scanning of the image medium as a reflectionsignal; converting the reflection signal in synchrony with the imagesignal into digital reflection values R(z,φ); determining from thereflection value R(z,φ) a correction value C(z,φ) to be associated withthe image-point; and scaling the image values image-point-wise with thecorrection values; producing a reference image by surface homogenousradiation of an image medium; separately processing images taken on theimage medium after or before the reference image by at least one ofmeans of the stored reflection values R_(R)(z,φ) or image valuesB_(R)(z,φ) of the reference image or data derived therefrom; anddetermining correlation data (a_(k),K) from the image values B_(R)(z,φ)and reflection values R_(R)(z,φ) of the reference image, and correctingthe image values B(z,φ) of a work image according to the magnitude ofthe stored reference values R(z,φ); wherein the image values B(z,φ) ofwork images are corrected according to the formula B′(z,φ)=B(z,φ)·[a_(k) ·F ₂ ⁻¹ {F ₂ {R _(R)(z,φ)}·K(u,v)}]⁻¹ wherein B′(z,φ) correspondsto the corrected image value of the work image, a_(k) and K(u,v)corresponds to the determined correlation data, F₂ corresponds to thetwo dimensional Fourier transform and F₂ ⁻¹ corresponds to an inversetransformation.